Blend doors and heat

[Briaineo]

2003 Jeep Grand Cherokee 2.7 CRD

Hi

Would anyone have any info on the workings of the heating system in the jeep

I have checked both in and return pipes under the bonnet for temp and both are hot ( heater core okay then?)

I removed the glove box and noticed the previous owner already had replaced the blend doors with a metal lever system (one of which broke off)

So I removed both blend doors and I thought I would then have heat but only the very slightest bit coming through!

[Adrian D]

They blend airflow coming through the heater core (hot) with air bypassing the heater core (outside temp).
My guess is that the heater core is a restriction to flow, so most of the airflow is bypassing the heater core.

[Jonny Jeep]

Looking at the FSM, the blend door controller is the same as used in TJs after the cable operation was removed.

The motors, in TJs at least, can gum up due to old grease and stop working. The motors can be removed, cleaned and regreased. Here's the page from the FSM describing the blend door removal. Bear in mind that this will be for a LHD model so where left and right are mentioned I would assume they are reversed, if like the TJ the HVAC system in the RHD is a mirror image of the LHD.